1. Field of the invention
The present invention relates to fluid pressure relief valves.
Relief valves are conventionally used in fluid pressure systems for the purpose of protecting the fluid pressure generating equipment, such as a cylinder, cylinder heads, bolts, pump valves, packing or cups, so that, in the event of malfunction or closing an external valve in error or excessive pressure as caused by a clogged drilling bit, the relief valve is biased to an open fluid discharge position enabling the operators to correct the malfunction without damage to the equipment.
There is an important need in industry to protect sample cylinders and bottles of gas. This invention provides a pressure relief valve for such equipment.
2. Description of the Prior Art
Fluid pressure relief valves presently in use and as disclosed by prior patents generally relate to valve structure which includes a valve stem or mandrel moved longitudinally in response to predetermined fluid pressure which shears a pin or ruptures a frangible disk, or the like. The pressure setting in which these valves open to release such pressure is predetermined by the pressure necessary to shear the shear pin or rupture the frangible disk. The pressure at which such a valve opens is thus predetermined by the known rating or shearing force required to shear a pin or rupture a frangible disk of predetermined thickness.
Shear type valves are dangerous in that they can be rendered inoperative by a workman, tired of resetting the valve, putting more than one shear pin or nail through the shear bar on one type safety relief valve or using extra strong metal, such as an Allen wrench through the shear stem in another type shear relief valve. Rupture disks have the disadvantage of being difficult to service in the field after rupture.
At present, the pressure relief valve used for the above mentioned cylinders or bottles is a rupture disk. The rupture disk relief valve has several disadvantages. First, it is extremely inaccurate, having accuracies on the order of .+-.20%. Also, the disk is difficult to seal in the disk housing so that there is the constant danger of leakage around the edge of the disk itself. Secondly, the disk has the tendency to fail early after constant use due to fatigue. This results in a loss of fluid in spite of the fact that the "set" or predetermined rupture pressure value had not been reached.
This invention provides a relief valve in which an axial pin or strut maintains the relief valve closed and is released by excessive pressure allowing axial movement of a piston-type valve and an opening of the relief valve.